Cochise County resident Lynn Kartchner, who wears a sidearm, tests a modified military searchlight that he uses to look for illegal activity at night in Arizona.

Lourdes Medrano

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Douglas, ARIZ.

If night and the high mountains that enclose the San Bernardino Valley are the greatest allies of drug smugglers trying to cross the US-Mexican border, then Lynn Kartchner intends to become one of the smugglers' worst enemies.

A shop owner who has sold guns to alarmed ranchers and seen one of them die – perhaps at the hands of a smuggler – Mr. Kartchner is setting up on random nights on the property of six local ranchers along the border. With him is a military searchlight fitted with night-vision scopes and a siren. The idea is simple: Find smugglers and call the border patrol – and if trouble starts, be ready.

Kartchner's effort echoes far beyond Arizona's Cochise County, which one expert calls "ground zero of the American vigilante movement."

From the alleged murder of a tourist on Texas' Falcon Lake by Mexican pirates to the killing of Kartchner's rancher friend, Robert Krentz, in March, there is a growing perception along America's southern border – sometimes at odds with statistics – that the US government is powerless to stop drug violence from crossing the border.

To some, the idea of armed civilians is a bad answer. "I'm not saying this guy would murder someone, but he might get confronted in a way that guns are pulled and people are shot," says Mark Potok of Alabama's Southern Poverty Law Center, which documents border vigilantism.

This has been particularly true in Cochise County since the mid-1990s, when tightened border enforcement began shifting illegal activities from urban areas into far-flung desert terrain. In 2005, for example, the county spawned the Minuteman Project, a controversial attempt to have neighborhood-watch-like citizen patrols on the border.

Cochise County is part of the busy, 262-mile Tucson sector, which boasts the most manpower along the 2,000-mile Southwest border and yields 40 to 50 percent of marijuana seizures, according to the border patrol.

But statistics present a mixed portrait of the region today. Border apprehensions in the Tucson sector dropped from 616,000 in fiscal 2000 to 241,000 in fiscal 2009. The violent crime rate in Arizona as a whole is falling, and homicides in Cochise are steady.

Border patrol Agent Mario Escalante says the area has experienced a "great change" since he was assigned to work it back in 2000. Back then, "There were people crossing all over the place," he notes. Now, pressure from additional manpower, fencing, and high-tech tools such as remote video surveillance have pushed illegal traffic westward.

Indeed, the Tucson sector is the most guarded along the international border. The number of agents here more than doubled to 3,300 between fiscal 2000 and fiscal 2009. In the past few weeks the region also got more than 500 of the 1,200 National Guard troops sent by the Obama administration to assist in border operations.

But seizures of marijuana – the drug most commonly confiscated – rose from about 240,000 pounds in 2000 to 1.2 million pounds in 2009 in the sector. In Cochise County, meanwhile, burglaries rose 10 percent from 2008 to 2009 (362 to 403).

This is where Kartchner is looking to step in – without getting too close. His gadgets, after all, can detect targets as many as four miles away. "Once we know where [smugglers] are and we've got them spotted, we'll crank on the light and call the border patrol," he says.

Kartchner has not yet come across illegal activity during his surveillance of various points of the valley. But one night, he was surprised to see a heavy border patrol presence a half-mile from the border – hovering helicopters and a National Guard observation post.

"At least for now," he says. "We must've touched a nerve in Washington."

The death of Mr. Krentz, in particular, increased the sense of urgency here. The case remains unsolved, but investigators suspect the rancher may have encountered a smuggler. If true, it would be the first time in at least 20 years that a rancher had been killed by an illegal border-crosser.

Ranchers' growing frustration and fear "pretty much came to a head with the Robert Krentz homicide," says Carol Capas, a spokeswoman for the Cochise County Sheriff's Department.

Data tell only a part of the impact of illegal immigration, she adds. For those far from the border, it is difficult to imagine waking up to find large groups of people huddling in the yard or coming home to find the house ransacked, but "these things are real to the citizens of Cochise County," Ms. Capas says. "It's something that they have to face all the time."

Five of the ranchers who have given Kartchner permission to use their ranchland "have had their homes broken into within the last 1-1/2 years," Kartchner says. He vows to make sure that no one on his nighttime rounds breaks any laws. And as long as they don't interfere with border patrol operations, they can be helpful by reporting suspicious activity, says Agent Colleen Agle. But "if they're going to take the law into their own hands, that's not going to help us," she says.

For his part, Sheriff Dever wants all hands on deck. "Anybody that wants to cross the border today, can," he says. "And until we can say that's not the case, then our border is not secure."